Fluidic conduit with repeated disturbance of laminar flow

The present invention relates to a fluidic device.

In liquid chromatography, a fluidic sample and an eluent (liquid mobile phase) may be pumped through conduits and a column in which separation of sample components takes place. The column may comprise a material which is capable of separating different components of the fluidic analyte. Such a material, so-called beads which may comprise silica gel, may be filled into a column tube which may be connected to other elements (like a control unit, containers including sample and/or buffers) by conduits.

When a fluidic sample is pumped through a cylindrical capillary, the Hagen-Poiseuille effect results in a non-uniform velocity profile along a cross-section of the cylindrical capillary and hence of the fluidic sample. Hagen-Poiseuille\'s law is a physical law concerning the voluminal laminar stationary flow of a viscous liquid through a cylindrical tube with constant circular cross-section. The said non-uniform velocity distribution over the conduit cross-section may result in longitudinal spreading of the zone containing analytes and thus in an undesired deterioration of the separation performance due to band broadening of different fractions of a separated sample.

Knitted Open Tubular reactors are designed to provide an efficient reagent mixing and/or a reaction delay in liquid chromatographic post-column reactions, while preserving the bandwidth of the separated peaks (see http://www.sequant.com/default.asp?ML=11513).

H. Engelhardt, U. D. Neue, “Reaction Detector with Three Dimensional Coiled Open Tubes in HPLC”, 1982 Friedrich Vieweg & Sohn Verlagsgesellschaft mbH, pp. 403-408 discloses a reaction detector with non-segmented flow in open tubes as reaction track. To minimize peak broadening, the open tubes are arranged in a three dimensional coiled structure by knitting.

U.S. Pat. No. 5,032,283 discloses a fluid conduit including a three-dimensional tube having a two-dimensional serpentine opening therethrough and exhibiting low peak dispersion which is applicable as an extra-column connection. The serpentine is a continuously curving path having periodic peaks and valleys of substantially uniform amplitude.

However, dispersion effects may still limit performance of fluidic measurement devices which are to be manufactured with a reasonable effort and in a reasonably small dimension.

It is an object of the invention to provide an efficient fluidic device. The object is solved by the independent claims. Further embodiments are shown by the dependent claims.

According to an exemplary embodiment of the present invention, a fluidic device is provided, the fluidic device comprising a planar (for instance having a basically two-dimensional extension) fluidic conduit for conducting a fluid (such as a liquid and/or a gas, optionally having a solid component), wherein the fluidic conduit has a plurality (that is two or more) of flow disturbance features located along at least a section of the fluidic conduit for disturbing a laminar flow of the fluid along the section (particularly when the fluid is pumped along the section, for instance with a high pressure of at least 600 bar).

According to another exemplary embodiment, a method of manufacturing a fluidic device is provided, the method comprising forming a planar fluidic conduit (for instance by etching a planar substrate) for conducting a fluid, wherein the fluidic conduit has a plurality of fluidic disturbance features located along at least a section of the fluidic conduit for disturbing a laminar flow of the fluid along the section.

The term “planar fluidic conduit” may particularly denote a fluidic conduit for conducting a fluid which is formed two-dimensionally or basically two-dimensionally. Two dimensions which may correspond to a plane of a substrate in which the planar fluidic conduit may be formed as a groove may define a trajectory along which the planar fluidic conduit may extend in a continuous manner so that a fluid can be conducted along a defined path in a two-dimensional space. The third dimension of the planar fluidic conduit may be defined by a depth of a groove in a substrate which may be constant along the planar fluidic conduit, thereby not disturbing the planarity. Thus, the planar fluidic conduit may define a fluid flow trajectory which may be arranged within a plane. In contrast to a planar fluidic conduit, a knitted capillary defines a three-dimensional trajectory such as a helical trajectory. In a planar fluidic conduit, a center of mass of a homogeneous fluid conducted through the fluidic conduit may perform a flow characteristic in accordance with a trajectory which lies within a plane. The fluid conduit may comprise multiple planar segments located in different planes of the planar structure, which segments can be interconnected.

The term “fluidic disturbance feature” or “low disturbance feature” may particularly denote any specific feature which intentionally disturbs a laminar flow of the fluid along the section or destroys the Hagen-Poiseulle\'s flow velocities distribution in the capillary. Such a fluidic disturbance feature may be formed by a wall shape, defining or delimiting the planar fluidic conduit, which may be specifically shaped or designed to redirect a flowing direction of fluid components to promote fluid mixing within a cross-section thus equilibrating the effective velocities of each fluid segment throughout a cross-section and thereby suppressing dispersion effects. However, a fluidic disturbance feature may also be a member provided separately from a wall as a mechanical obstacle positioned within the fluidic path and forcing the fluid to deviate from its former or its undisturbed flowing profile, thereby contributing to turbulent impacts on the fluid flow.

According to an exemplary embodiment, the conventional shortcoming of a limited resolution of a fluid separation system such as a liquid chromatography system due to dispersion effects caused by an inhomogeneous velocity profile of a fluid flowing along a linear conduit may be efficiently suppressed by intentionally arranging multiple fluid disturbance features along the fluid path, thereby disturbing a laminar flow. This disrupts or disturbs a parabolic flow profile in accordance with Hagen-Poiseuille\'s law and therefore equilibrates a velocity profile of different components or segments of the fluid. This may efficiently suppress dispersion effects and may therefore allow to increase the efficiency or resolution of a sample separation system such as liquid chromatography system. At the same time, the formation of a planar structure in a substrate together with repeated fluidic disturbance features may allow for a very simple and hence cheap architecture for designing dispersion-suppressing conduits.

Next, further exemplary embodiments of the fluidic device will be explained. However, these embodiments also apply to the method.

The plurality of fluidic disturbance features may be adapted for disrupting a laminar flow of the fluid along the section. In other words, an intentional destruction of a Hagen-Poiseuille flow velocity profile may be performed to thereby—repeatedly—prevent the system from formation of local zones characterized by Hagen-Poiseuille-like flow profile. By this, dispersion will be reduced since the formation of a pronounced velocity profile may be prevented.

While conventional approaches usually intend to keep a disturbation of a fluid flowing along a channel as small as possible, exemplary embodiments take contrary measures by intentionally disturbing the fluid flow multiple times. Particularly, a trajectory defining a fluid flow or a center of gravity thereof may follow a line approaching a mathematical non-differentiable function.

The plurality of fluidic disturbance features may promote a turbulent flow of the fluid along the section. Thus, the shape, size and orientation of the fluidic disturbance features may be selected so that a transfer from a laminar flow to a turbulent flow can occur or fluid velocity components laying in the plane of a conduit cross-section arise. A laminar flow may relate to a scenario in which the fluid is moving smoothly along a path or around an object. A fluid flow may become turbulent when being forced to flow around obstructions such as posts or pillars. Turbulence or turbulent flow may be a flow regime characterized by chaotic, stochastic property changes. This may include low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and/or time. The dimensionless Reynolds number may characterize where the flow conditions lead to laminar flow or turbulent flow. For instance, a flow having a Reynolds number above 4000 may be denoted as a turbulent flow, whereas a flow characterized by a Reynolds number below 2100 may be considered as a laminar flow. In a range between 2100 and 4000, a transitional flow characteristics may be assumed.

The fluidic conduit may be delimited by a boundary surface which is defined by a mathematical function which is not differentiable at least one position. More precisely, such a mathematical function may be a trajectory of a wall of a fluidic conduit delimiting the fluid flow in a plan view. In mathematics, a derivative may be denoted as the velocity of change of a property. A derivative may be denoted as an instantaneous velocity of change and can be calculated at a specific instant rather than as an average over time. The process of finding a derivative may be called differentiation. Even if a mathematical function is continuous at a point, it may not be differentiable there. A function is not differential at a specific position when it is not possible to unambiguously calculate a value of the derivative here. At a position at which a function is not differentiable, the function may have a sharp bend, and at this point the derivative may make a jump. Regarding fluid dynamical properties of such a bend, it may promote a turbulent redirection of a fluid component hitting a wall portion associated with such a non-smooth trajectory position. The plurality of fluidic disturbance features may be formed as wall portions located so that a portion of the fluid hits against this wall portion to thereby promote mixing with another portion of the fluid. This may reduce or cancel out undesired dispersion effects.

Additionally or alternatively, the plurality of fluidic disturbance features may comprise one or more mechanical obstacles, particularly pillars or posts, within a fluid path which force(s) the fluid to flow around the at least one mechanical obstacle. Such obstacles may be connected at a wall defining or delimiting the fluid path which allows for a secure connection of the obstacles at a fixed position. It is also possible that such mechanical obstacles are arranged within the fluidic channel without being fixed to the wall, for instance embedded in a packing material for fluid separation, such as embedded in a matrix of chromatographic beads. In such a scenario, the obstacles may be kept in place by a pressuring force between components of the filling material and walls of the fluidic channel.

The planar fluidic conduit may comprise repeated fluidic disturbance features within the section to provide for a repeated fluidic disturbance along this section. Repeated fluidic disturbance features may be arranged in accordance with a specific sequence, for instance periodically. Thus, an ordered structure of disturbing features may be designed introducing sufficient dispersion prevention and at the same time maintaining a sufficiently high fluid flow velocity.

The fluidic disturbance features may be arranged or located along the section in accordance with a pattern, which may be a one- or two-dimensional pattern, or even a three-dimensional pattern. A one-dimensional pattern may relate to the arrangement of obstacles or specific curvature features of the wall along a straight line, for instance at a constant distance from one another. A two-dimensional arrangement may be for instance the arrangement of obstacles or specific wall features in a direction of the fluid flow and in a direction perpendicular thereof, for instance a matrix-like arrangement of obstacles in rows and columns. A three-dimensional pattern may also involve a direction perpendicular to the planar channel, for instance obstacles located on a top wall and on a bottom wall of the channel, not or not only on side walls thereof.